HBV is a lethal virus which causes acute or chronic viral hepatitis in human body and finally makes progress to liver cancer. Though the vaccines against the virus have been developed, a therapeutic agent has been hardly developed yet. Up to the present, Ara-A or interferon has been partially used for the treatment of hepatitis B, but both agents have many problems in their activity and safety.
Recently, a variety of nucleoside compounds having anti HBV activity have been reported.
For example, it is reported that 2',3'-dideoxy-3'-thiacytidine [Proc. Natl. Acad. Sci. USA, 88, 8495 (1991)], 5-fluoro-2', 3'-dideoxy-3'-thiacytidine [Proc. Natl. Acad. Sci. USA, 88, 8495 (1991)], 2', 3'-dideoxy-.beta.-L-5-fluorocytidine [Biochem. Pharm., 47, 171 (1994)], and 2', 3'-dideoxy-.beta.-L-cytidine [Biochem. Pharm., 47, 171 (1994)] have anti-HBV activity.
However, these compounds leave much to be improved in view of their activity and safety, whereby development of novel compounds having more activity and less toxicity has still been required.